If you need for the pressing of one button to lock out other buttons, I recommend a "game show circuit" (sometimes called a Jeopardy circuit) that is external to the PC. Polling multiple buttons through a serial or USB port adds time delays and ambiguities that can invalidate the results. If you are talking about audience response buttons, where there is a large quantity but timing data is not critical, then one option is a large long serial string, but again I'd recommend some external multiplexing circuit to take some of the load off the PC. Once accurate button data is inside the PC, it's all "just software".
ak